The present invention relates to an apparatus for retrieving pipe sections from a well bore, and in particular relates to a releasable spear for retrieving pipe sections from a well bore such as an under-sea well bore.
It has been proposed to provide a spear for retrieving sections of a pipe from a well bore. The spear has a radially expandable cutter adjacent the bottom, and immediately above the cutter an expandable grapple. The grapple is firmly connected to the drill string and thus rotates with the drill string. A marine swivel is also mounted on the drill string at a position above the grapple to rest on top of the pipe section being cut.
When a pipe section is to be cut the described spear is inserted into the upper end of the pipe until the marine swivel rests on the top of the pipe. This enables the drilling string tension created by the weight of the spear to be released. The drill string is then rotated to enable the cutter to cut the pipe and the grapple, located inside the pipe, may be expanded to grip the inside of the pipe. After the pipe has been cut the severed part of the pipe is brought to the surface by applying tension to the drilling string.
The prior proposed spear has the disadvantage that it can only be utilised to retrieve relatively short sections of a pipe at a time, and if a long section of pipe has to be retrieved, severe difficulties may be encountered. Also it is to be noted that the drilling string is relaxed during the cutting process, thus making it necessary to provide a marine swivel, which is relatively expensive.
The present invention seeks to provide an improved apparatus for retrieving a pipe from a well bore.